Use AppendData to add a newly fetched packet of records from a provider to the client dataset. Data indicates the packet of records to add. HitEOF indicates whether the provider encountered the end of the dataset when it fetched the records from the database server. 

Most applications call GetNextPacket instead to fetch a packet of records and automatically add them to those already available. Use AppendData when fetching data packets directly from the provider rather than letting the client dataset fetch data. 

GetNextPacket 

TDataSetProvider